Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   "Graf (AWS), Alexander" <graf@amazon.de>
To:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "rkrcmar@redhat.com" <rkrcmar@redhat.com>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "Schoenherr, Jan H." <jschoenh@amazon.de>,
        "Raslan, KarimAllah" <karahmed@amazon.de>,
        "Lukaszewicz, Rimas" <rimasluk@amazon.com>,
        "Grimm, Jon" <Jon.Grimm@amd.com>
Subject: Re: [PATCH v2 04/15] kvm: x86: Add per-VM APICv state debugfs
Thread-Topic: [PATCH v2 04/15] kvm: x86: Add per-VM APICv state debugfs
Thread-Index: AQHVU4YAxicok8C98kOOsiSZW3JVFacCQeaAgAujmoCAANQngIACP0YAgAAPr4U=
Date:   Wed, 28 Aug 2019 19:36:03 +0000
Message-ID: <9A47CE02-18B0-40C3-962A-D317A32F2073@amazon.de>
References: <1565886293-115836-1-git-send-email-suravee.suthikulpanit@amd.com>
 <1565886293-115836-5-git-send-email-suravee.suthikulpanit@amd.com>
 <a48080a5-7ece-280d-2c1f-9d3f4c273a8d@amazon.com>
 <049c0f98-bd89-ee3c-7869-92972f2d7c31@amd.com>
 <f9c62280-efb4-197d-1444-fce8f3d15132@amazon.com>,<1bfccb79-5ace-0dba-a201-e069f77f740a@amd.com>
In-Reply-To: <1bfccb79-5ace-0dba-a201-e069f77f740a@amd.com>
Accept-Language: en-US
Content-Language: de-DE
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> Am 28.08.2019 um 20:41 schrieb Suthikulpanit, Suravee <Suravee.Suthikulpa=
nit@amd.com>:
> =

> Alex,
> =

>> On 8/27/19 3:20 AM, Alexander Graf wrote:
>> =

>> =

>>> On 26.08.19 21:41, Suthikulpanit, Suravee wrote:
>>> Alex,
>>> =

>>>> On 8/19/2019 4:57 AM, Alexander Graf wrote:
>>>> =

>>>> =

>>>>> On 15.08.19 18:25, Suthikulpanit, Suravee wrote:
>>>>> Currently, there is no way to tell whether APICv is active
>>>>> on a particular VM. This often cause confusion since APICv
>>>>> can be deactivated at runtime.
>>>>> =

>>>>> Introduce a debugfs entry to report APICv state of a VM.
>>>>> This creates a read-only file:
>>>>> =

>>>>>      /sys/kernel/debug/kvm/70860-14/apicv-state
>>>>> =

>>>>> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
>>>> =

>>>> Shouldn't this first and foremost be a VM ioctl so that user space =

>>>> can inquire its own state?
>>>> =

>>>> =

>>>> Alex
>>> =

>>> I introduce this mainly for debugging similar to how KVM is currently =

>>> provides
>>> some per-VCPU information:
>>> =

>>>       /sys/kernel/debug/kvm/15957-14/vcpu0/
>>>           lapic_timer_advance_ns
>>>           tsc-offset
>>>           tsc-scaling-ratio
>>>           tsc-scaling-ratio-frac-bits
>>> =

>>> I'm not sure if this needs to be VM ioctl at this point. If this =

>>> information is
>>> useful for user-space tool to inquire via ioctl, we can also provide it.
>> =

>> I'm mostly thinking of something like "info apic" in QEMU which to me =

>> seems like the natural place for APIC information exposure to a user.
> =

> I could not find QEMU "info apic". I assume you meant "info lapic", =

> which provides information specific to each local APIC (i.e. per-vcpu).

Or maybe even "info kvm" :). I think you get the point.

> =

>> The problem with debugfs is that it's not accessible to the user that =

>> created the VM, but only root, right?
> =

> Hm, you are right. I'll also look into also adding ioctl interface then.

Thanks!

Alex


Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Ralf Herbrich
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879